public class Test {
    static long count = 0;
    synchronized static public void add () {
        count++;
    }
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(()->{
            for (int i = 0; i < 10000; i++) {
                add();
            }
        });
        Thread t2 = new Thread(()->{
            for (int i = 0; i < 10000; i++) {
                add();
            }
        });
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println(count);

    }
}
